System of mercury vapor lighting



O MICROSECONDS MICROSECONDS INVENTOR. HERMAN O. S-roeurme QZ LA-r-roauezv Fte. L

nite @tate SYSTEM F MERCURY VAPR LTGHTING Herman O. Stoeltng, Milwaukee,Wis., assigner to McGraw-Edison Company, a corporation of DelawareApplication January 17, 1955, Serial No. 482,0i7

9 Claims. (Cl. 315-122) This invention relates to lightning protectingmeans for series circuit mercury vapor lamps.

in series systems of mercury vapor lighting damage from lightningfrequently occurs. This damage may be to the film cut-out placed inparallel with each of the lamps or to the lamp itself due to thelightning surge. it is the usual practice to ground some portion of theseries loop, for example, the middle portion or that portion most remotefrom the constant current supply means such as a constant currenttransformer for instance. Under these conditions it is apparent thatwhen lightning strikes some portion of the circuit the surge isdischarged at the grounded portion but has to travel past a number ofmercury vapor lamps before it arrives at such grounded portion andconsequently the various elements constituting the series loop aresubjected to high voltages for a period measured in microseconds.

The film cut-out or puncturable lm device is relatively inexpensive butit is a troublesome element to replace as it not only requires theservices of a lineman but also because it is frequently placed in arather diiiicultly'accessible position, for example, in the lamp socketitself and thus requires a considerable amount of labor to replace it.The lm cut-Out itself is not very expensive but the time loss and thelabor consumed constitutes a marked disadvantage.

Damage to the mercury vapor lamp itself by lightning is veryobjectionable as these lamps are relatively eX- pensive.

Damage from lightning can occur either when the merv'cury vapor lampsare operating or when the circuit is deenergized. In both cases thelightning surge usually causes damage.

lt is difcult to protect mercury vapor lamps due to the fact that theyhave a negative resistance current characteristic, the resistancefalling as the current in the lamp increases. Thus it is ditiicult togenerate suicient voltage to cause sparkover for a protecting lgap evenif a protecting gap is placed in shunt with each lamp. Consequentlyvoltage rise under these conditions usually cause puncture of the iilmcut-out if not damage to the lamp itself.

This invention is designed to protect mercury vapor lighting systemsagainst damage from lightning strokes no matter whether the rate of riseof the surge current due to the lightning is rapid or relatively slow,and a further and highly desirable object, in the preferred form of theinvention, is to provide such a type of lightning protection that itwill not only protect the lamp itself but it will also protect the Vfilmcut-out while in no way interfering with the normal and desirableoperation of the mercury vapor lamp or the lm cut-out.

Further objects are to provide lightning protecting means for mercuryvapor lamps which is relatively inex- -V-pensive and which may be easilyinstalled and which e occupies a relatively small amount of space.

It is Vimmediately apparent that due to the increase in A.voltage .dropacross mercury vapor lamps with an in- Patented Feb. 25, 1958 crease inrate of rise in surge current, that it is easier to protect the lamp bymeans of a spark gap during steep front surges than it is to protect thelamp for moderate rates of surge current rise. This invention howeverprovides protection for either type of lightning surge current so thatthe lamp and the lm cut-out as well, are both protected under allconditions irrespective of the type or rate of surge current rise asmeasured against microseconds, for instance.

A further specific object of this invention is to provide means forprotecting mercury vapor lamps against damage from lightning under bothconditions either when the lamp is operating or when the lamp is cold.

Embodiments of this invention are shown in the accompanying drawing inwhich:

Figure l is a diagrammatic view showing a mercury vapor series systemwith the invention applied thereto.

Figure 2 is an enlarged schematic detail of one of the units.

Figure 3 is a chart showing the relation between the voltage and timefor a mercury vapor lamp sparkover when the lamp is cold, for a tilmcut-out, and for a lightning arrester spark gap, when the lightningprotecting means is not used.

Figure 4 shows a series of curves indicating the rate of rise of surgecurrent and voltage across a lamp when the lightning protecting means isnot used.

Figure 5 shows a modified form of the invention.

Referring to the drawings it will be seen that a series system ofmercury vapor lighting has been indicated, in Figure l, and a singleunit has been illustrated in Figure 2, the latter iigure being drawn toan enlarged scale.

The mercury vapor lamps may be of any suitable type commonly used inseries circuit lighting systems. One form of commonly used mercury vaporlamp has a pair of main electrodes and a starting electrode closelyspaced from a main electrode and connected to the other electrodethrough a high resistor of the order of several megohms for instance.

The mercury vapor lamps, indicated by the reference character 10, areconnected in a series loop with some portion of the loop, forexample,the outer portion or mid-point, indicated at 11, grounded as indicatedat 12. The circuit is supplied from a high voltage source of alternatingcurrent, such as a substantially constant current transformer T. Thetransformer is preferably a static type, constant current transformer. Amoving coil type, though less desirable, can be used. The circuit isindicated by the reference character 13 and it will be seen that at eachof the mercury vapor lamps a spark arrester gap 14 and a film cut-out 15are bridged across the lamp, or in other words are arranged in parallelwith the mercury vapor lamp 10. However, it is to be noted particularlythat an impedance such as the resistor 16 is placed in series relationto the mercury vapor `lamp 10 and to the iilm cut-out 15. The spark gaphowever is not affected by the impedance or resistor 16 but is directlyin the circuit independently of the impedance.

It is within the scope of this invention to form the spark gap 14, thelm cut-out 15, and the impedance 16 as a unitary structure as indicatedby the dotted lines 17 of Figure 2.

While the following ligures are in no sense to vbe interpreted laslimiting they are given so as to show clearly what has been successfullyused for certain installations. For example, for a mercury vapor vlamprequiring 135 volts whileoperating and a current of 3.2 amperes, it hasbeen found that the impedance 16 may consist of a resistor of 1.5 ohms.It is again stated that these gures are not to be'interpreted aslimiting Abut g to the other.

t lain'p against surges, the impe'dances 16 hereinabove de Y Y scribedare placed in Vseries with the lamps and ilrn cut` outs so as toincrease the voltage drop suiciently to cause sparkover of theprotecting `gap 14. It is of course i' to be understood that`theimpedance maybe an Vin ductance, a capacitance, or several possiblecombinations and inductances or it may be arresistor. VThe preferred-embodimentis a resistor as shown and described for reasonthatfaninductance while it does not Vcause n 1a total loss ofY energy, has avoltage drop which is proportional to the rate of surge current rises.The inductance therefore has VVthe highestk voltage drop Vat theY.higher ratesof surge currentrise where itis Ynot so much neededvforprotection and thus becomes most eiective Vat'the Vsame. time Ythatspark gap Ybecomes most effective. On the other hand, a capacitor has animpedance which 'is roughly inversely proportional to theV steepnessrofthe front of the surge, somewhat analagous to the considerationsaffecting the impedance of the capacitor for high frequency phenomena.This type of characteristic while desirable for protection of mercuryvapor lamps is not `desirable for Ypassage of the V'ordinary 60 cyclesoperating current, `in the normal operation of the lamp, since acapacitor to be effective in lightning protectionA would *cause anexcessive `voltage drop during normal operation. In addition totthisboth the inductance and the capacitor have to be many timeslarger inphysical size than an effective andfsatisfactory resistor. Y t `Thespark Vgap contemplated by this invention would have togbe sov designedthatit is unaffected by the discharge of surgeV current whenV followedYbyV a power` current; ow not exceeding Yone-half cycle, for example,though variations in the design ofthe spark gap are of coursecontemplated by this invention. In other words, thersparkl gap would beso arranged that it would not be damaged yunder normal roperatingconditions.V t In order torassist in a clear appreciation of thesigniicance of the various components forming the lightning protectingmeans attention is directed to the Vcurves shown in Figures 3 and 4.Figure y3 shows for curve X, the sparkover voltage plotted against 'timefor the mercury Y vapor -lamp while the lamp is cold or in non-operatingcondition. `Curve -X does not indicate the normal starting voltage ofthe lamp, but indicates the undesirable condition when there isasparkover from one main terminal voltageand V'time forrlightningprotection Ywith a lm cutout. vCurve Z'fshowsAthe relationbetweenrvoltage and time for the spark-gap. Y

FigureV 4i1lustrates the relation between theV rate Yof rise of surgeVcurrent 'andthe voltage; The current is.V plotted in the Vreverse,direction `from the voltage merely for the sake of clearnessin thediagram. Y It is to be understood Vthat thevoltage wave shape'andfcrestmagnitude of both the current and voltage are not well establishedbecause of the wide range in current wave' Vshapes whichfare `possiblein a lightning surge.

only to convey theidea thatthere is a de'nit'e relationship between themaximum voltage droptand the rateof rise of I surge current." Thevoltage curves A, B, and C.V cor-Y Figure Y. shows the relation betweenVthe The `'figureV is intended n respond to surge current curves A, VB,'and' C. Y These curves shown in Figurell arefor a mercury vapor. lamp Yf which `i'snot equippedwith. the lightning protecting-means formingthesubject matter of this invention. i .v The curvesshown inv Figures 3and it'are not intended itybeV fabsolu'tely' accurate Vunder all'operating "conditions, llbutijarejlcrves obtained Vfrom laboratoryAmeasurements #and 'are'only relative. Due to variations in individualspecimens of lightning arrester spark gaps,'r`ner'cu`ry vapor;

4 lamps, and film cut-outs a more accurate representation would be byrelatively wide bands jrather than-by'single curves. Y Y

in the form of the invention shown in Figure 5, the impedance 16' isplaced in series with the mercury vapor lamp and not in series withthe'iilrn cut-out 15 as in the previously described form of theinvention. this construction the lilrn 'cut-out 15 would be subject tohigher impulse voltages than Vwith thecircuitrshown in` A t Figure 2 butthe proper operation of the circuit would .Y

stili be possible and practical though lthe form of the invention shownin Figure 2 is much the' preferred form. It is, however, to bedistinctly understood'thatztheform of: the invention shown in Figure 5is notV considered the equivalent of the form V'of the invention shownin Figure 2 Vand unquestionably the film cut-out 15 of Figure S is notprotected in the same manner as that shown in Figure 2. Y

It will be seen that nov'el and extremely simpleforrns of lightningprotecting means have beenV provided by this invention which may be mosteasily used and in-VV stalled in a series system of mercuryvaporlighting.

It is Vto be notedtparticularly that thoughthe construc-V tions areextremely simple and the component parts-relap Y Y tively inexpensivethat nevertheless these lightning protecting devices areV eminentlyVeffective in protecting against serious damage rto 4the mercuryjvapor1amp`s,rin t both forms of theV invention, and against 'inadvertentpuncture of the viilm cut-outs as well, Vin the preferred t form of theinventionpduring lightning surges.

VAlthough this invention has beenV described in considerable detail, itis to be understood .that suchd'escription is`intended as illustrativerather than lim1t1ng,`as"

the invention may beV variously embodied and is to'be interpreted asclaimed. l claim:

Vl. A series system Yof mercury vapor lighting comprising Y apluralityof mercury vaporV lamps connected-in series inaV 'mainline a sourceY` ofhighvoltage alternating current, a cut-out shunted across eachmercuryrvaporlamp for shortingV out any lamp upon failure thereofand'v'constituting.

a parallel'circuit with the corresponding lamp, an `impedance connectedin serieswith each parallel circuit and constituting therewith aVcompound circuit, and a spark gap directly iniseries with saidrmainline and bridging` each compound circuit consisting of the seriesimpedance and the parallel circuit. l'

2.A seriessystem of mercury vapor Vlighting havmga plurality of kunitsconnected in series in a main lineandV having a substantially constantcurrent high voltage source,

each unit consisting of a spark gap directly in serieswith said main1ine=and a parallel circuitbridging said spark Y gap and connected inseries withan impedance with the impedance located between one end ofthespark gap .and one end of the parallel circuit,peach of said parallelcircuits consisting of a mercury vapor lamp and a bridging cut-outshuntql across the lamp for shorting out the lamp upon failurey thereof.I j.

3. A -seriessystem of mercury vapor lighting having a plurality of unitsconnected inseries inta main line and having a substantially'constantcurrenthigh voltage source and havingagrounded portion, each unitconsisting of;a spark gap directly in series with said main linearnd aparallelY circuit bridging said spark gap and connectedinr'w;n

series with 'an impedance with the'impedance located between one endVofthe spark gap and one endofethe 'i parallel circuit, each of saidparallel lcircuits consisting of a mercury vapor lamjp 'and Va bridgingfcut-out`shunted` across said lamp Yfor shorting out therlamp upon.failure thereof. Y' Y' Y 4. A series'systern' of mercuryvaporlighting'having a"` pluralitytof units connected-in `se'riesinfiamainline and K- v having a substantially.constantcurrert high voltagesource'Y and having'a grounded portioneat a point remote front` Y saidsource, each unit'consisting'fof a sparkl gap directlyinVAX Y ,5 .71

With

series with said main line and a parallel circuit bridging said sparkgap and connected in series with an impedance with the impedance locatedbetween one end of the spark gap and one end of the parallel circuit,each of said parallel circuits consisting of a mercury vapor lamp and abridging cut-out shunted across said lamp for shorting out the lamp uponfailure thereof.

5. A series system of mercury vapor lighting comprising a plurality ofspark gaps connected in series, a separate circuit bridged across eachspark gap, each circuit consisting of a parallel circuit including amercury vapor lamp and a cut-out bridged across said lamp, and eachseparate circuit having an impedance connected in series with theparallel circuit between one end of the parallel circuit and the one endof the corresponding spark gap.

6. A series system of mercury vapor lighting comprising a plurality ofspark gaps connected in series, a separate circuit bridged across eachspark gap, each separate circuit consisting of a parallel circuitincluding a mercury vapor lamp and a cut-out bridged across said lamp,and each separate circuit having a resistor connected in series with theparallel circuit between one end of the parallel circuit and one end ofthe corresponding spark gap, said system having a grounded portion.

7. A series system of mercury vapor lighting having a plurality of unitsconnected in series in a main line and having a substantially constantcurrent high voltage source and having a grounded portion, each unitconsisting of a spark gap directly in series with said main line and aparallel circuit bridging said spark gap and connected in series with animpedance with the impedance connected between one end of the spark gapand one end of the parallel circuit, each of said parallel circuitsconsisting of a mercury vapor lamp and a bridging cut-out shunted acrosssaid lamp for shorting out the lamp upon failure thereof, said sparkgap, impedance and cut-out constituting a unitary structure.

8. A unit for a series system of mercury vapor lighting, said unitcomprising a mercury vapor lamp and a cut-out shunting said lamp and aspark gap in parallel with said cut-out and lamp and a resistorconnected between one side of said spark gap and said lamp and cut-out,said resistor being in series with said lamp and cut-out.

9. A series system of mercury vapor lighting comprising a plurality ofmercury vapor lamps connected in series in a main line, a source of highvoltage alternating current, a cutout slrunted across each mercury vaporlamp for shorting out any lamp upon failure thereof and constituting aparallel circuit with the corresponding lamp, an impedance connected inseries with each mercury vapor lamp and constituting with the mercuryvapor lamp and the cut-out a compound circuit, and a spark gap connectedin series with said main line and bridging each compound circuitconsisting of the series impedance and the parallel circuit.

Reerences Cited in the le of this patent UNlTED STATES PATENTS 430,096Waddell June 10, 1890 1,884,789 McCombes Oct. 25, 1932 1,960,408 BrachMay 29, 1934

